Heat-treating and cold-rolling hadfield manganese steel



Patented Sept. 7 1948 QHEA'I THEATING AND COLD-ROLLING .HAIDFIEIJDIMALNGANESE STEEL Carl W; Weesner, Warren, Ohio, and Wallace B. Llfingwell; Sharon, Elvan .R. Babylon, New Wilmington, 'and'Homer'L. .Schell; Sharon, Pa;, assignorstofih'a'ron SteelUorporation, Sharon, Pa a'corp'orationofiPennsylvania .NoiDrawing. Applicationlibecember 16, 1943, Serial No. 514,548

The invention relates to :the 'manufacture'of manganese'steel strips and" the'ilike; and more particularly to the manufacturepf: thin fgauge, cold rolled; high manganese, high carbon steel strips and the like adapted 'toiheuse'd'iamong other purposes i or making helm'etsff'or the armed forces.

Helmet steel must'be soft, ductile-and have-deep drawing qualities in order thathelmets may-be properly formed or drawnto' the 'desiredshape from high manganese "steel. High manganese or Hadfield steel, thatisgsteel containingirom 10% to 20% manganese and'from'1100'% to 150% carbon as thin as .044 to inch, an'd'co'ld rolled and heat treatedis admirably suitedfor' such purposes. However, extreme difficulties have been encountered'and considerable damaged or scrap' material h'asqb'een made in attempts to manufacture-such material.

Some of these difficulties andwhat is belleved to be the explanation-of the-"causes of the same are set forth in the copending WeesnerandIieffingwell applications Which-have matured-as Patents Nos. 2,368,9525' and 2,410;3 2 2i Howeveiythe inventions describ'e'd in sai'd 'Weesner and Letfingwell patents are directed more particularlyto ways and means :of reclaimingprsalvagingsuoh damaged high-manganese strip material.

The present invention involves the avoidance or elimination of the conditions Which apparen'tly cause the material to be damaged during the cold rolling and heat treatment thereof." Thus, the difficulties or damage-apparentlyare caused in part by sur fa'ce :embrittlement resultlng" from decarburization.

In our early attempts-at cold-rolling and heat treating Hadfield strip two conditions were iound associated with low ductility -first, :oarbid'e precipitation at "grain boundaries, and, second,

frosty surface, i. e. the-:fros'ty appearance re- -40 sulting from innumerabiesmall cracks developed by the Olsen ductility cup test.

We discovered that the-icarbide"precipitation .difficulties could'abe controlled lbyea very careful v control of the cooling or quenching 'stage ofi the heat treatment :step.

Tests maderevealedr-thattheiirostyisurfiaceiwas accompanied :by decarburlzatio'n. :Samples known to be frosty and decarburized: were-rel car-burized and heat treated .verylcarefully nnder controlled laboratory conditions and" TbhBlIi'hEStEd. After the recarburizing- :heat treatment, the

,=frosty conditiondisappeared andthe ductility-'ras determined bythe-Glsen cup-test, wasimaterially increased. Thus, it was finally determinedithat i- 2 the frosty surface embrittlem'entis the resultiof decarburization.

In most steels, lowering the carbon content tends toward softness and ductility, 'butf-Hadfield steel behaves in a ,contrary'manner; "'Iheductility of Hadfieldst'eel when pr'esentisdue t o'its austenitic composition. When the-carbomcontent is "considerably lowered; the 'highmanganese austeriite is no longerstable on cooling, but-tends to'decompose, probably forming a'brittle mixture of epsilon and alpha'iron.

"Unfortunately, it is hardly-possible-and not practical in the commercial manufacture Y of thin gauge high manganese, high carbonst-ritvsteol to recarburize material which' has'b'ecome decarburized, in order to correot 'theponditionsifourrd to exist, as-shown by recarbur-izatiow of -samples in-labor-atorytests; so itbe'cameabsoliitely essentia'lto find some way in which vtheideoarburiza- 'tion during heat treatment could be elimirrat'ed.

The normal heat treating cycleufor Hadfiel'd steels includes heating the steel to a itemperature above the upper critical .point, approximately .1800 F. to-1900 :F. and usually about- 18509!! and then-quickly cooling the :same, .as ss'etztorth insaid Weesner and Lehingawelll patents.

We have discovered that Hadfieldzsteel :responds .tozheat treatment: extremely :rapidly' and that thet'steel is completely austenitizedazalmost instantaneously upon being ,heated' towaaeliigh temperature of from 1900" vF; to 20.00 21?..3and preferably from 1950 F. to 2000 Frintavfiumaee in which the temperature is maintainedrim the hottest'lzone at approxiniatelyflflofl rF;: andrthese furnace and steel temperatures .arematerially higher than those :previousl iusedwforwheatxtmatin pl-ladfield steels.

We have further discovered that-tthe extentrof decarburization occurring in 'l-ladfield steel; which is the-cause of the dimculties; is proportional to time and that if the steel is substantially -in- .stantaneously completely .austenitized .by .ex-

. tremely rapid heating totne-high tempe'ratureof "preciable amount of decarburization to .occur.

It is therefore possible by 'heatingand; quenching at high "speeds, that is by carefully "controlling the time and temperature of "heating, to hold 'sur'face decarburization of Hadfild steePto-"Sueh a minimum that no harmful effects result.

We have further discovered that the sufl-a'ce appearance rof cold .rolled .heat treatedililadfield steel is no reliable index as touthepresenoe :Ior absencewof surface decarburization cor :embrii';tles

ment. If the heat treatment is carried out in a highly oxidizing atmosphere, there is a tendency to scale and "burn the surface of the Hadfield steel strip at the same time that the decarburization and surface embrittlement occurs. Continued heating of Hadfield steel in a non-oxidizing neutral or moderately reducing atmosphere will produce a decarburized and brittle surface without appreciable scaling or marring of the surface. Thus, a good surface does not necessarily indicate good ductility or the absence of decarburization and surface embrittlement. Continued heating in a very reducing atmosphere, however, produces very little surface decarburization.

Test samples made in the laboratory from the same material were heated for 5 minutes at 1950 F. in three different atmospheres, water quenched and tested. The first sample was heated in a highly oxidizing atmosphere and when tested had a .390 Olsen cup test value with a frosty con- ;dition. The sample also had heavy decarburization with a rough surface, burned and scaled, and very brittle.

The secondsample was heated in a moderately reducing atmosphere. When tested it had a .390 0lsen'cup test value with a frosty condition. The surface Was heavily decarburized and brittle, butthe surface appearance was smooth,

The third sample was heated in a very reducing atmosphere and when tested had a .440 Olsen cup test value with no frost. The surface condition was smooth, there was very little decarburization and the sample was ductile.

Therefore, the character of the furnace atmosphere during the heat treatment is also an im ,portant factor in addition to the control of the time and temperature of heating. Unfortunately, in mill practice it is not feasible to maintain a highly reducing atmosphere in continuously heating cold rolled Hadfield steel strip as rapidly as it is necessary to do so followed by an immediate quench. For these reasons, it is only possible as a practical matter to control the furnace atmosphere such that it is non-oxidizing, neutral or moderately reducing, which can ordinarily be readily done in the operation of fuel fired continuous heat treating furnaces by a proper control of the burners and of the fuel air ratio. When the furnace atmosphere is thus controlled, and

. when the heat treating is very rapidly carried out,

little if any surface decarburization, burning or scaling occurs.

Accordingly, it is an object of the present invention to provide a method of manufacturing thin gauge, cold rolled, high manganese, high carbon steel strips and the like Without surface decarburization or embrittlement, so that the normal ductile properties of austenitic manganese steel may be obtained.

A further object of the present invention is to provide a method of making cold rolled, heat I treated, high manganese steel in accordance with strip practice cold rolled to gauges as thin as .044

to .033 inches in thickness.

'Furthermore, it is an object of the present invention to provide a new method of manufacturing cold rolled, high manganese steelstrips and the like by which the resulting product has a good surface appearance, extreme toughness and strength, and high ductility and drawing qualities.

And finally, it is an object of the present invention to provide a new method of making cold rolled, light gauge, high manganese strip steel 4 and the like more quickly and more cheaply than it has been produced previously.

These and other objects may be obtained, the stated results achieved, and the described difiiculties overcome by the methods, steps, products, treatments, and discoveries which comprise the present invention, a preferred outline of the steps being set forth in the following detailed description, and which are particularly and distinctly pointed out and set forth in the claims forming part hereof.

High manganese, high carbon strip steel of the Hadfield type is hot rolled down to the thinnest possible gauge to which it can be rolled without damaging the strip or hot mills, which may be approximately .109 inch in thickness, and the strip is then coiled and cooled in water as rapidly as possible to prevent carbide precipitation and decomposition. This cooling step following hot rolling is a departure from usual methods which do not ordinarily include such a step in connection with the manufacture of hot rolled strip.

The hot rolled strip is then continuously heat treated to take the carbides back into solution and to render the steel fully and uniformly austenitic. The heat treatment is performed in accordance with the discoveries of the present invention by substantially instantaneously completely austenitizing the steel by extremely rapid heating to a temperature of from 1900 F. to 2000 F., preferably in the latter half of said range, followed by immediate water quenching;

Thus, the heat treatment of 17 /8" x .109" and of 15%" x .109 hot rolled Hadfield steel has been successfully accomplished in accordance with the present invention in a 25 foot continuous heating furnace in which a non-oxidizing, neutral or moderately reducing atmosphere is maintained, and in which the furnace temperature is maintained at or above approximately 2000* F. The effective interior length of this furnace is approximately 23 feet and the hot rolled strip having the widths and gauge stated have been run at from 9 to 12 feet per minute through the furnace. The strip reaches a temperature close to the furnace temperature of approximately 1950 to 2000 F. at a point approximately 2 feet ahead of the furnace exit opening. The strip is then water quenched as quickly as possible by passing it into a water quenching bath immediately as it leaves the furnace.

As previously pointed out, the cycle of the extremely rapid heating followed by an immediate water quench occurs so quickly that there is no opportunity for surface decarburization of the material to occur.

The strip is then pickled in an inhibited sulphuric acid pickling bath, preferably an aqueous solution of about 10% sulphuric acid by weight in Water operated at a temperature of about F.; and the strip is then water sprayed, washed, steam jetted and dried in a hot air drier.

We have also discovered that the pickling step is somewhat critical and particularly the pickling temperature, because Hadfield steel burns or pits at a higher pickling temperature and the drying step is necessary to prevent rusting and to eliminate hydrogen for preventing hydrogen embrittlement.

The strip may then be cold rolled from the nominal .109 gauge down to .075 to .080 gauge (31% to 27% reduction, or about 27% reduction) on a four stand tandem cold rolling mill; Other The above operations of heating or annealing,

i quenching. pickling and cold rolling:- are then repeated to.reduce the 1 strip from- .075 to. .080

, gauge .d-own to .050. to: .055: gauge; and again to reducethe' strip from .050 to .055 gauge down 'to .044ito. .048 gauge to makethe finished cold rolled material; or: even'againto reduce the strip from .0441to .048 gauge down to .033 to .038 gauge finishedimateriala The-"first intermediate anneal after the materiallhas been: coldrol'led to from-.075 to 080 gauge is carried out with a strip speedthrough the annealingflfurnace described of: about 12. feet penminute; the secondintermediate anneal or heatitreatment."is..:carried out at .a stripspeed through thefurnaceo-f about 18 feet per-minute, the.tl1ird "intermediate anneal is carriedout at a strip speed of about 30 feet per minutaand the lais'tiiintermcdiate anneal. is carried. out at a speediof. BOJKfeetperm-inute or higher;

Thus; in each instance, the heat treatment is carried r-out; in. the shortest possible time at the fastest possible rate. of. heating; and the quench isaperform'ed as quickly as possible after leaving the heatutr'eating. furnace.

The heat: treating, operations. in each instance are: controlled to. accomplish several results: first, to recrystallize the cold rolled structure, second, toxkeep: the carbides: in. solution, and third; to prevent:- surface decarburizatio-n or embrittlemerit. The-heating to the high temperature between 1900 13. and2000 F. recrystallizes the cold rolled-structure, theimmediate Water quench k'eps the 'carbides insolution, and the rapidity of. heating. and quenching prevents. decarburization'; The resultingmaterialis fully and uniformly austenitic with carbides in solution, with the cold rolled structure recrystallized, and without any. objectionable decarburized surface layers.

We have discovered thatif for some reason the heat treating operation is slowed down, for instance, because of-some failure of equipment, or of: the necessity vof stopping the line for welding one coil to another, thus permitting portions of the strip to lie in the furnace, these portions will have badly decarburized surfaces and these portionsvmust be removed. However, the material therein may be reclaimed by treatment such as describedzirreither of the Wee'sner and Leffingw'ell companion patents referred to.

While the-process and product have beenidescribed in connection with the manufacture, of strip steel: or stripsheets made in accordance-With strip practice, the, present invention is also applicable to the manufacture of other high manganese steel... products such as sheet steel, in accordance with sheet practice.

Accordingly, when the term strips is used hereinland-in-the appended claims, the term is intended to include the manufacture of cold roiledihignmanganese steel. strips, stripsheets, sheet-s wire andthe like.

Also, when/the term high'manganesesteel is referred to herein, it means steels of'the Hadfield type, which generally contain from to 20% manganese and from 1% to 1.5% carbon, with possible additions of small percentages of other alloying elements, such as nickel and chromium, which sometimes are added to Hadfield steels.

Thus, the present improvements and discoveries provide for the ready and economical manufacture of high manganese steel strips cold rolled to gauges as thin as .044 to .033 inches having extremely high ductility characteristic of fully? austenitic manganesemsteel'gi and zwithout surfaces"decarburizationsor embri'ttlementz.

Having? newt-described: theafeatures; oftthe': inventiom: an embodiment :of; steps l by-iiwhich the inventionrmayrbeecarried out, the: advantages and "results attained by. :the:ainvention-, and. the new discoveries mader in: connection with the treatments of and-cold rollingrof high-manganese steel; the. new" and useful: methods, steps; treatments,. arrangements; and-products, (are set forth in the appended 'claims.

We claim&* a

1. The; method of producing; strong 1 metal sheets of: hot-rolled Hadfield -manganesesteel,

has elapsed for the i-occurrence of 'surface decarburization" quickly; water quenching the continuously moving stripimmediately as ita'leav-es the furnace, to keep the carbides: in: solution, and then: cold rolling the .strip .down. to 0.0575 to 0.080, thick strip 3. The 7 method of -.making cold rolled Hadfield manganese steel: strip ,glessthan 0.109 in :thickness; having a. fully;,.,and uni-formly austenitic structure :with carbideshin solution, and being free of surfacer-decarburization and; embrittlement; which comprises, completely austenitizing 0.109 thick; hot rol-ledI-Iadfield manganese steel strip by. heatingr-the strip. as: it-moves continuously-through a: furnace to a strip temperature of :1900" Fwto 2000? R, .then bef.ore sufficient time has elapsed for the occurrence; or -surface decarburization quickly water quenching i the continuously .moving strip immediately: .asitleaves the furnace-to keep the, carbideslin' solution, then cold rolling-the "strip; down: to -i 0.075 to 0.080 thick strip; and then repeating-the: beating quenching and acold: rolling ,operations until i the strip reduced 1170 0.044?! to:,0.033" thickmaterial.

i; The :methodi of: making :cold rolled Hadfield manganese steel strip having a a fully A and uniformly; austenitic-i-structure with" carbides in solution; and. being; free of. surface decarburization,; and--embrittlement; ...which' comprises, completely austenitizingi ,Ha'dfield' manganese steel strip: by extremely rapidly. heating; the is strip; I as it moves continuously;. through a furnacetov a strip: temperature? of. 1950 -'F.-- to 120009 V F-, then beforesufli cienttimechasr. elapsedrfo'r'the occur rencetor surface decarburization quickly: water quenching the continuously moving stri r imm'eidiately as it leaves the furnace to keep the carbides in solution, and then cold rolling the strip to about 25% reduction.

5. The method of making cold rolled Hadfield manganese steel strip having a fully and uniformly austenitic structure with carbides in solution, and being free of surface decarburization and embrittlement; which comprises, completely austenitizing Hadfield manganese steel strip by extremely rapidly heating the strip as it moves continuously through a furnace toa strip tem perature of 1950 F. to 2000'F., then before sufficient time has elapsed for the occurrence of surface decarburization quickly water quenching the continuously moving strip immediately as it leaves the furnace to keep the carbides in solution, then cold rolling the strip to about 25% reduction, and repeating the heating, quenching and cold rolling operations until the strip is reduced to 0.044" to 0.033" thick material- 6. The method of making coldrolled Hadfield manganese steel strip having a fully and uniformly austenitic structure with carbides in solution, and being free of surface decarburization and embrittlement; which comprises, completely austenitizing Hadfield manganese steel strip by extremely rapidly heating the strip in a nonoxidizing atmosphere as it moves continuously through a furnace to a strip temperature of 1950 F. to 2000 F. to substantially instantaneously obtain complete austenitization of the steel at said temperature, then before sufflcient time has elapsed for the occurrence of surface decarburization quickly water quenching the continuously moving strip immediately as it leaves the furnace to keep the carbides in solution, and then cold rolling the strip to about 25% reduction.

7. The method of making cold rolled Hadfield manganese steel strip having a fully and uniformly austenitic structure with carbides in solution, and being free of surface decarburization and embrittlement; which comprises, completely aiu'stenitizing Hadfield manganese steel strip by extremely rapidly heating the strip in a non-oxidizing atmosphere as it moves continuously through a furnace to a strip temperature of 1950 F. to 2000 F. to substantially instantaneously obtain complete austenitization of the steel at said temperature, then before sumcient time has elapsed for the occurrence of surface decarburization quickly water quenching the continuously moving strip immediately as it leaves the furnace to keep the carbides in solution, then cold rolling the strip to about 25% reduction, and repeating the heating, quenching and cold rolling operations until the strip is reduced to 0.044" to 0.033" thick material.

8. The method of making cold rolled I-Iadfield manganese steel strip, less than 0.109" in thick ness, having a fully and uniformly austenitic structure with carbides in solution, and being free of surface decarburization and embrittlement; which comprises, completely austenitizing 0.109" thick hot rolled Hadfield manganese steel strip by extremely rapidly heating the strip continuously during 21 feet of strip travel at from 9 to 12 feet per minute in a non-oxidizing atmosphere in a furnace to a strip temperature of 190 F. to 2000 F., then before suin'cient time has elapsed for the occurrence of surface decarburization quickly water quenching the continuously moving stripimmediately as it leaves the furnace to keep the carbides in solution, and then cold rolling the strip to 0.075" to 0.080" thick strip.

8 9. The method of making cold rolled Hadfield manganese steel strip having a fully and uniformly austenitic structure with carbides in solution and being free of surface decarburization and embrittlement; which comprises, hotrolling Hadfield manganese steel strip to the thinnest possible hot rolled gauge, then rapidly water cooling the strip, then completely austenitizing the steel by extremely rapidly heating the strip as it moves continuously through a furnace to a strip temperature of 1950 F. to 2000 F., then before sufficient time has elapsed for the occurrence of surface decarburization quickly water quenching the continuously moving strip immediately as it leaves the furnace to keep the carhides in solution, and then cold rolling the strip to about 25% reduction. 7

10. The method of making cold rolled Hadfield manganese steel strip having a fully and umformly austenitic structure with carbides in solution and being free of surface decarburization and embrittlement; which comprises, hot rolling Hadfield manganese steel strip to the thinnest possible hot rolled gauge, then rapidly water cooling the strip, then completely austenitizing the steel by extremely rapidly heating the strip as it moves continuously through a furnace to a strip temperature of 1950 F. to 2000 F., then before sufiicient time has elapsed for the occurrence of surface decarburization quickly water quenching the continuously moving strip immediately as it leaves the furnace to keep the carbides in solution, then cold rolling the strip to about 25% reduction, and then repeating the heating, quenching and cold rolling operations until the desired cold rolled gauge is obtained.

CARL W. WEESNER.

WALLACE B. LEFFINGWELL.

ELVAN R. BABYLON.

HOMER L. SCHELL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 938,893 Potter Nov. 2, 1909 1,017,904 Potter Feb. 20, 1912 1,344,392 Hadfield June 22, 1920 1,462,460 Apgar July 17, 1923 1,851,903 Hall Mar. 29, 1932 1,929,356 Janitzky Oct. 3, 1933 2,368,955 Weesner et al. Feb. 6, 1945 2,378,991 Franks June 26, 1945 OTHER. REFERENCES "High Manganese Austenitic Steels, reprinted from The Iron Age issue of Oct. 1, 1942, Electro Metallurgical (30., N. Y. C.

Alloys of Iron and Chromium, vol. II, Kinzell and Franks, 1940, pp. 289, 438, 442, and 443.

Metals Handbook, 1939 ed., pages 1133, 1134, 1135, and 568. 

